1. Field of the Invention
The present invention relates to a bearing load measuring system for separating and measuring the radial load and load moment acting on bearings in a rotary machine using rotary type bearings that have rolling bodies.
2. Description of the Related Art
Space transport systems that are more economical than the systems currently in use will be required in future space activities, and there is currently a strong demand for the realization of reusable space transport systems. Judging from existing technology, it is realistic to expect that liquid fuel rocket engines will be used as the propulsion systems in such cases. One of the most important constituent elements in such liquid fuel rocket engines is the turbo-pump. In order to realize reusable space transport systems, a higher reliability and longer useful life than those currently seen will be required in such turbo-pumps. However, in the case of rocket turbo-pumps in which smaller size and lighter weight have been pursued in accordance with a desired increase in speed, radial vibration caused by unstable fluid forces is a problem in extending the useful life. The reason for this is that excessive radial vibration causes a drop in durability, and at the same time leads to fatal accidents. Accordingly, it appears that if it were possible to measure the radial load generated by radial vibration, the information obtained by such measurement could be effectively utilized in a soundness monitoring system, or to establish measures for suppressing radial vibration.
The radial load measuring system that is the object of the present invention is a system that uses the bearing cartridge in a turbo-pump as a load cell, and that makes it possible to measure the radial load without causing an increase in weight or any great variation in the vibrational characteristics of the rotary shaft system. Such a technique for measuring the load acting on a bearing utilizing this bearing cartridge has shown results when used in the liquid oxygen turbo-pumps of the main engines of the United States Space Shuttle; however, all of the loads measured have been treated as radial loads. This bearing load measuring cartridge is shown in FIG. 1. The rotating part of the bearing is constructed from an inner race 2 which rotates together with the shaft, and an outer race 3 which is non-rotating together with the bearing cartridge 1, with bearing balls 4 interposed [between the two races]. However, the physical quantity measured in this case is actually a load in which the radial load and load moment are combined; in a conventional system of this type, separate measurement is impossible. Furthermore, in research conducted in the past by the present group of inventors, it was found as a result of investigation in experiments performed using a bearing cartridge (shown in FIG. 2) of more or less the same type as the bearing cartridge in the LE-7 liquid oxygen turbo-pump in the first-stage main engine of the H-2 rocket that the output of the strain gauge tends to be affected by the positions of the bearing balls.
It is an object of the present invention to provide a system which makes it possible to measure radial loads using the bearing cartridge in a turbo-pump as a load cell without causing any increase in weight or great variation in the vibrational characteristics of the rotary shaft system, wherein the radial load and load moment acting on the bearing can be separately measured without the output of the strain gauge being affected by the positions of the bearing balls.
The bearing load measuring system of the present invention is a system that measures bearing loads using a bearing cartridge as a load cell. This bearing cartridge is constructed as a double-cylinder type cartridge consisting of an inside cylindrical part that contacts the bearing on the inside, and an outside cylindrical part that is connected via a ring-form supporting member. The bearing load is measured by strain gauges that are disposed on the surface of the abovementioned outside cylindrical part. Furthermore, the positions in which the strain gauges are disposed are set as two points at which the phase of the strain is different and the strain is large from the relationship between the amount of strain and the position on the upper surface of the cartridge in the axial direction when a specified load is applied in the radial direction in an analysis by the finite element method, and which satisfy the condition that there is little effect when the load moment is varied by varying the load application point in the axial direction. Moreover, the attachment position in the axial direction of the ring-form member that connects the inside cylindrical part and the outside cylindrical part is determined using the minimal effect of the load moment of the strain in the circumferential direction as a standard.
Furthermore, the number of strain gauges is set as a number consisting of a plurality of sets disposed in the circumferential direction, with each set consisting of a pair of strain gauges in positions in which the phase is different in the axial direction, and the attachment position in the axial direction of the ring-form member that connects the inside cylindrical part and the outside cylindrical part is determined using the minimal effect of the load moment of the strain in the circumferential direction as a standard.
Strain gauges are disposed on the outer surface of the outside cylindrical part in axial positions that receive the maximum effect of the load moment, and the load moment is measured from the difference in output between these strain gauges and strain gauges disposed in positions where the effect of the load moment is minimal.